1. Field of the Invention
The present invention relates to an internal-combustion-engine control apparatus, and particularly to an internal-combustion-engine control apparatus provided with an exhaust gas sensor control device having an abnormality-determination function for an exhaust-gas sensor that detects the air-fuel ratio of an exhaust gas.
2. Description of the Related Art
The result of detection, of an air-fuel ratio, by an exhaust-gas sensor that detects the air-fuel ratio of an exhaust gas is utilized in an air-fuel ratio control system configured with an engine control unit (referred to as an ECU, hereinafter) and the like; the foregoing result is utilized in order to realize, for example, stoichiometric combustion control in which an air-fuel ratio is feedback-controlled in the vicinity of the stoichiometry (theoretical air-fuel ratio), lean combustion control in which an air-fuel ratio is feedback-controlled in a predetermined lean region, and the like.
In the foregoing air-fuel ratio control system, it is strongly requested to expand an air-fuel ratio detection range so as to enable air-fuel ratio detection in a wide region and to raise the accuracy of detection of an air-fuel ratio in the range. As a technology of this kind, there has been disclosed a technology in which an amplification factor or an offset voltage for a detection signal obtained a gas sensor element is selected on a timely basis by an amplification circuit so that, in the case where a low amplification factor is selected, a wide-range output corresponding to a wide air-fuel ratio range can be obtained, and in the case where a high amplification factor is selected, a narrow-range output corresponding to a narrow air-fuel ratio range can be obtained (for example, refer to Japanese Patent Laid-Open Pub. No. 2006-275628 (paragraph 0009, FIG. 1)).
However, as disclosed in Japanese Patent Laid-Open Pub. No. 2006-275628, in the case where an amplification circuit performs switching of the amplification factor thereof or the offset voltage thereof so as to detects an air-fuel ratio signal, for example, there has been a problem that, when an abnormality in the amplification circuit causes an abnormality in the air-fuel ratio signal, no appropriate air-fuel ratio control can be performed, whereby the exhaust gas is deteriorated.